Lead Lag Control System for Water Heaters

ABSTRACT

A control system is shown for a series of two or more water heaters arranged in parallel. A cold water supply line delivers cold water from a cold water source to a cold water inlet at each of the respective two or more water heaters arranged in parallel. A low pressure restriction is present at each cold water inlet of the water heaters which presents a low pressure restriction to the flow of cold water at each cold water inlet. A by-pass valve is also present at the cold water inlets for by-passing cold water from the cold water supply line around each of the low pressure restrictions. A hot water discharge line receives and discharges hot water from each of the water heaters. A controller is used to control when each of the by-pass valves will be open or closed based upon demand with only the by-pass valves being open which are needed to meet demand placed upon the system.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from the earlier filed provisional application, Ser. No. 62/089,597, filed Dec. 9, 2014, entitled “Lead Lag Control System for Water Heaters.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to water heater systems and control methods for water heaters and, more specifically, to a simplified lead lag, control system for a series of two or more water heaters arranged in parallel.

2. Description of the Prior Art

Water heaters are used in a large variety of residential, commercial and industrial settings. For example, large storage tank systems are often found in hospitals and institutions, industrial plants, schools, universities, apartment complexes, and the like. The different types of water heaters which are used to supply hot water to these systems may use various sources of energy, such as gas, oil, electricity, boiler water or steam. For example, in conventional gas/oil fired water heaters, hot gas flows through a series of vertically mounted tubes which are mounted in vertical fashion between top and bottom support plates within the water heater tank. Water flows into and out of a chamber located between the support plates and contacts and circulates about the exterior of the vertical tubes to effect heat transfer to heat the water.

U.S. Pat. No. 4,465,024, issued Aug. 14, 1984, and assigned to the assignee of the present invention describes another type of water heater which has a submerged, pressurized combustion chamber so that all combustion occurs in the water heater tank interior in a chamber surrounded by water, thereby reducing heat loss and increasing efficiency. These two examples are merely intended to be illustrative of the various types of gas/oil fired water heaters which exist in the prior art.

Because the demand for hot water tends to vary over time in most installations, it is generally necessary to provide some sort of control over the heat source or flow rate through the device to accommodate the varying flow rates of the water being heated. In most applications the temperature of the water to be heated varies dramatically according to the time of year, and other factors. For example, a typical domestic hot water system is only under demand about 10-20% of the time. Additionally, in most applications the quantity of water flowing through the water heater varies according to the time of day and use patterns of the application. Thus, the water heater outlet water temperature must be regulated in order to accommodate variability resulting from the inlet water temperature and flow rate changes.

Most water heaters are capable of delivering water at a desired temperature in steady state conditions where the water demand or flow rate is substantially constant. However, water heating systems presently available or prior art water heating systems sometimes fall short when attempting to maintain a water output at a constant predetermined temperature level during rapid shifts or during fluctuations in water demand. As a result, during a rapid increase in water demand, a user might experience a sudden drop in water temperature or a cold water splash. Conversely, during a rapid decrease in water demand, a user might experience a sudden spike in water temperature.

Control systems are known for water heating systems having, for example, two or more water heaters arranged in parallel fashion which utilize large motorized control valves along with complicated electronic controllers to control the cycling of the water heaters. However, starting up and shutting down each water heater is inefficient due to the pre-purge and post-purge operations involved. Also, there is no reason to operate, for example, three water heaters when one would meet the demand. In the prior art system, the controller senses temperature and opens or closes the large valves. It also decides which water heater will return to service first. So, for example at night when demand is low, only one heater might be on-line. This system certainly works, but the large motorized valves are expensive. If they fail, they have the potential to shut down the hot water system in the building. The electronic controller is also somewhat expensive. The logic/sensing of when and how many to have open can be complicated.

The present invention has as an objective to provide a simplified and improved control system for a series of water heaters (not boilers), having two or more water heaters in parallel. It might be used in a hospital, university campus setting, apartment building, hotel, and the like.

SUMMARY OF THE INVENTION

A control system is shown for two or more water heaters arranged in parallel. The improved control system includes a cold water supply line which delivers cold water from a cold water source to a cold water inlet at each of the respective two or more water heaters arranged in parallel. A forward bias check valve is present at each cold water inlet of the water heaters, which presents a low pressure restriction to the flow of cold water at each cold water inlet. A by-pass valve is provided for by-passing cold water from the cold water supply line around each of the check valves. A hot water discharge line receives and discharges hot water from each of the water heaters. A controller is present which controls when each of the by-pass valves will be open or closed based upon demand with only the by-pass valves being, open which are needed to meet demand placed upon the system.

Preferably, the by-pass valve is a motorized valve controlled by an electrical signal and the controller is selected from the group consisting of lead lag timer, another type of lead lag controller and a device for emitting a control signal where the control signal is used to control the by-pass valves. Preferably, the lead lag controller comprises a programmable timer for determining when each of the by-pass valves will be open or closed. The controller can also be manually set to determine which by-pass valves are open.

In one preferred configuration, the forward bias check valve has an open forward pressure of less than about 1.5 psi, most preferably on the order of 0.5 psi. When demand is met by one bypass valve being open, only water from one water heater is being used. The system compensates for increased demand by an associated pressure drop across the check valves and the bypass valves, causing the check valves to open until demand is met.

Additional objects, features and advantages will be apparent in the written description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of a prior art control system for a series of water heaters arranged in parallel using motorized control valves.

FIG. 2 is a schematic diagram similar to FIG. 1, but showing the improved control system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred version of the invention presented in the following written description and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples and as detailed in the description which follows. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the principle features of the invention as described herein. The examples used in the description which follows are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those skilled in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention.

As has been briefly discussed, the present invention concerns an improved control scheme for two or more water heaters (not boilers), having two or more water heaters in parallel. It might be used in a hospital, university campus setting, apartment building or hotel, etc.

FIG. 1 attached shows a prior art control system for commercially available water heaters 10, 12, 14 which receive cold water from a cold water supply line 16 and discharge hot water from a discharge line 18. The prior art system uses large motorized control valves 15, 17, 19 and a complicated electronic controller 21 to control the cycling of the water heaters. Those skilled in the relevant arts will appreciate that starting up and shutting down each water heater is inefficient due to the pre-purge and post-purge operations involved. Also, there is no reason to operate three water heaters when one would meet the demand, etc. In the prior art system, the electronic controller 21 senses temperature and opens or closes the large valves 15, 17 and 19. It also decides which water heater will return to service first. So, for example at night when demand is low, only one heater might be on-line. This system certainly works, but the large motorized valves 15, 17, 19 are expensive. If they fail, they have the potential to shut down the hot water system in the building. The electronic controller 21 is also somewhat expensive. The logic/sensing of when and how many to have open can be complicated.

FIG. 2 is a simplified schematic diagram which shows the control system of the invention, which accomplishes the previously described control task in a simplified and somewhat more mechanical fashion. The cold water supply line delivers water from a suitable water source (not shown) to the cold water inlet 25, 27, 29 of each of the water heaters in the system. Each of the cold water inlets also has a forward bias check valve 31, 33, 35 plumbed into the line. These valves will open at a low forward water pressure, typically less than about 1.5 psi and more preferably on the order of about 0.5 psi. Each check valve also has a significantly smaller motorized by-pass valve 37, 39, 41 associated with it, These by-pass valves might be, for example, ¾ inch valves. The small valves cost on the order of 1/20 that of the large motorized valves of the prior art. They can be controlled by a simple lead-lag timer 43 or other lead-lag controller or control signal. The by-pass valves could even be manually set. It is also likely that, at some point, each of he check valves 31, 33, 35, and its associated by-pass valve 37, 39, 41, will be incorporated into one small body.

An invention has been provided with several advantages. The control system of the invention provides a much less complicated and consequently less expensive control system than those system presently on the market. Instead of sensing anything, the present system places a low pressure restriction in the cold water inlet lines (the forward bias check valve) with a by-pass being placed around the restriction. When the demand is net by one bypass valve opening, only water from one heater is being used. The other water heaters are hot, but have no hot water demand and don't cycle, The system automatically compensates for increased demand when, for example, more people turn on faucets in the building, the pressure drop across the open valve and the check valves will increase, allowing the water to flow through the check valves. If a motorized valve becomes stuck open or closed, the system would not be lead-lag, but hot water would still be available. So, in summary, instead of using electronics and sensing temperature, the new system controls flow without worrying about temperature; the system only sets a lead heater for all of the low flow.

The purpose of the check valve is to have a pressure gate. A standard plunger with spring check valve typically has a 0.5 psi crack open forward pressure before flow will start. Future implementation may use other devices than a forward bias check valve to provide this pressure gate in place of the check valve.

As has been mentioned, it will be appreciated by those skilled in the art that the system could operate with manual valves, as well. Also, although the preferred description which follows shows the invention on the cold water side of the heaters, there is no reason that it cannot be applied to the hot water side. In other words, from the hot water outlet, to each check valve/bypass valve, and the outlet of each check valve/bypass valve joined together to feed the building load. Also, most building applications have a reticulation pump or pumps. These pumps could be configured to return to each heater at the return inlet connection, not to the cold water supply.

As an example of operation of the system, assume pressure restricting device is configured to start opening at 1 PSI of pressure, and the Cv value of the bypass valve is 10 GPM (10 GPM at a 1 PSI pressure drop across the valve). With a bypass valve open on the lead heater, then a system load in the range of 0-10 GPM would be satisfied by the one open bypass valve, and all the hot water usage would be from the one lead heater. The other heaters would simply be maintaining heat on the water in their tanks. The lead heater would be receiving all the cold water, and would cycle on for sooner and stay on longer in this situation. The result would be a reduction in the number of heater cycles used and therefore improved efficiency. As usage increases above 10 GPM, then the pressure drop across the bypass valves and check valves will increase over 1 PSI; the check valves will start opening, providing hot water from all the heaters. Still, the lead heater will have less restriction and will be providing slightly more of the load than any other single heater. The benefit is that during low load situations, there will be a decrease in the number of total cycles, thereby reducing the number of heaters cycling, improving efficiency and lowering energy usage.

While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof. 

What is claimed is:
 1. A control system for two or more water heaters arranged in parallel, the control system comprising: a cold water supply line which delivers cold water from a cold water source to a cold water inlet at each of the respective two or more water heaters arranged in parallel; a flow restricting element present at each cold water inlet of the water heaters, the flow restricting element presenting a low pressure restriction to the flow of cold water at each cold water inlet; a by-pass valve for by-passing cold water from the cold water supply line around each of the flow restricting elements; a hot water discharge line which receives and discharges hot water from each of the water heaters; a controller which controls when each of the by-pass valves will be open or closed based upon a selection of a lead heater with only one bypass valve being open which are needed to meet low demand situations placed upon the system.
 2. A control system for two or more water heaters arranged in parallel, the control system comprising: a cold water supply line which delivers cold water from a cold water source to a cold water inlet at each of the respective two or more water heaters arranged in parallel; a forward bias check valve present at each cold water inlet of the water heaters, the forward bias check valve presenting a low pressure restriction to the flow of cold water at each cold water inlet; a by-pass valve for by-passing cold water from the cold water supply line around each of the check valves; a hot water discharge line which receives and discharges hot water from each of the water heaters; a controller which controls when each of the by-pass valves will be open or closed based upon selection of a lead heater with only one bypass valve being open which are needed to meet low demand situations placed upon the system.
 3. The control system of claim 2, wherein the controller is selected from the group consisting of lead lag timer, a lead lag controller and a device for emitting a control signal.
 4. The control system of claim 2, wherein the controller is manually set to determine which by-pass valves are open.
 5. The control system of claim 2, wherein the forward bias check valve has an open forward pressure on the order of 0.5 psi.
 6. The control system of claim 2, wherein the system uses manually operated valves instead of motorized valves.
 7. The control system of claim 6, wherein the system compensates for increased demand by an associated pressure drop in the system causing the check valves to open until demand is met.
 8. A control system for two or more water heaters arranged in parallel, the control system comprising: a cold water supply line which delivers cold water from a cold water source to a cold water inlet at each of the respective two or more water heaters arranged in parallel; a forward bias check valve present at each cold water inlet of the water heaters, the forward bias check valve presenting a low pressure restriction to the flow of cold water at each cold water inlet, each of the forward bias check valves having an open forward pressure which does not exceed about 0.5 to 1.5 psi; a motorized by-pass valve for by-passing cold water from the cold water supply line around each of the check valves; a hot water discharge line which receives and discharges hot water from each of the water heaters; a lead lag controller which controls when each of the motorized by-pass valves will be open or closed based upon selection of a lead heater with only the by-pass valves being open which are needed to meet demand situations placed upon the system.
 9. The control system of claim 8, wherein the lead lag controller comprises a programmable timer for determining when each of the by-pass valves will be open or closed.
 10. The control system of claim 9, wherein when demand is met by one bypass valve being open, only water from one water heater is being used.
 11. The control system of claim 10, wherein the control system compensates for increased demand by an associated pressure drop in the system causing the check valves to open until demand is met. 